This invention generally relates to a miniaturized chemical processing apparatus, and more specifically, to a miniaturized chemical processing apparatus assembled from stacked plates that cooperate to provide fluid channels for conveying reactants and other fluids.
Methods of controlling and optimizing processes for producing chemical compounds are well known. The control of parameters such as temperature, pressure, mixing conditions, relative volumes of the reactants, and the use of catalysts are generally well understood. Traditionally, newly discovered chemical compounds and processes involving either the production of such compounds, or processes involving the use of such compounds, have been initially carried out by researchers in xe2x80x9cbench-scalexe2x80x9d environments. Particularly promising chemicals or processes may ultimately be produced in quantity by application to industrial scale processes. Often, problems are encountered in scaling up a process from the laboratory to industrial scale production.
Problems associated with moving from bench-scale production to industrial scale production often involve changes in process conditions between the bench-scale environment and the industrial environment. For example, the temperature of the reactants within a small beaker or flask in a laboratory is much easier to keep constant than the temperature within a production tank having a capacity of hundreds of liters, as is often the case in a chemical processing plant. Variations in other process conditions within a large tank are also more difficult to control, and frequently effect the quality and yield of the desired product.
Another aspect of laboratory development of processes to produce chemical compounds is that often potentially dangerous chemicals are used to create the desired product. Fires and explosions in research laboratories and concomitant injury to personnel and property are well known risks in the chemical research industry. The risks are not limited only to research only, as industrial chemical production facilities also may experience fires and explosions related to chemical production using dangerous chemicals. Often, due to the quantities of chemicals used in industrial scale processes, such accidents are significantly more devastating in an industrial setting than similar accidents in a research setting.
Recently, much attention has been directed to the use of micro-scale reactors for both development and production of chemical processes. These types of reactors offer several advantages. As noted above, the control of chemical processes within very small reactors is much simpler than control in a large-scale production tank. Once a reaction process has been developed and optimized in a micro-scale reactor, it can be scaled up to industrial production level by replicating the micro-scale reactors in sufficient quantity to achieve the required production output of the process. If such reactors can be fabricated in quantity, and for a modest cost, industrial quantities of a desired product can be manufactured with a capital expenditure equal to or even less than that of a traditional chemical production facility. An additional benefit is that because the volume of material in each individual reactor is small, the effect of an explosion or fire is minimized, and with proper design, an accident in one reactor can be prevented from propagating to other reactors.
Safety in the research setting is also improved, as such reactors generally require less exposure to hazardous substances and conditions by research personnel than traditional xe2x80x9cwet-chemistry,xe2x80x9d which typically requires that the researcher physically handle chemicals in a variety of glass containers, often in the presence of an open flame and/or other heat sources. Any accident in such an environment is likely to increase the risk that the researcher will be exposed to hazardous chemicals, as well as the risk of causing significant damage to the laboratory. In contrast, small scale or microreactors can be designed as self-contained units that minimize the researcher""s potential exposure to chemical substances. Since when using a microreactor, the researcher is not required to physically manipulate containers of chemical materials to carry out a desired reaction, the reactor can be located in an area so that if an accident should occur, any resulting fire or explosion can be relatively easily contained.
Another area in which microreactors offer an advantage over conventional chemical process development and production is in the mixing of reactants. A mixing channel of the proper scale encourages a laminar flow of the reactants within the channel and is readily achievable in a microreactor. A laminar flow enhances mixing by diffusion, which eliminates the need to expend energy to physically stir or agitate the reactants and is an extremely fast and efficient mixing technique.
Microreactors particularly offer great promise to the pharmaceutical industry, which engages in chemical research on many new chemical compounds every year, hoping to find a drug or chemical compound with desirable and commercially valuable properties. Enhancing the safety and efficiency of such research is valuable in and of itself. And, when coupled with the potential that these reactors offer for eliminating the problems of moving from bench-scale production to industrial production, it will be apparent that a microreactor suitable for use in carrying out a variety of chemical processes and having an efficient and low-cost design will be in high demand.
Several different designs for microreactors have been investigated. For example, such reactors are described in U.S. Pat. No. 5,534,328 and U.S. Pat. No. 5,690,763 (both listing Ashmead as the inventor). These patents describe reactors structures for chemical manufacturing and production, fabricated from a plurality of interconnected layers. Generally, each layer has at least one channel or groove formed in it and most include orifices that serve to fluidly connect one layer to another. These layers are preferably made from silicon wafers, because silicon is relatively inert to the chemicals that may be processed in the reactor, and because the techniques required to mass produce silicon wafers that have had the required channels and other features etched into their surfaces are well known.
A disadvantage of the reactors described by Ashmead stems from the rather expensive and complicated process for manufacturing the devices. While silicon wafer technology is advanced to the state that wafers having desired surface features can readily be mass produced, the equipment required is capital intensive, and unless unit production is extremely high, the substantial costs are difficult to offset. While Ashmead does suggest that other materials can be used to fabricate the layers, such as metal, glass, or plastic, the surface features required (grooves, channels, etc.) must still be formed in the selected material. The particular surface features taught by Ashmead require significant manufacturing steps to fabricate. For instance, while forming an opening into a material is relatively easy, forming a groove or channel that penetrates only part way through the material comprising a layer is more difficult, as the manufacturing process must not only control the size of the surface feature, but the depth, as well. When forming an opening that completely penetrates through a material comprising a layer, depth control does not need to be so precisely controlled. Ashmead teaches that not only openings that completely penetrate the layers are required, but also that surface features (grooves/channels) that do not completely penetrate the individual layers are required. Hence, multiple processing steps are required in the fabrication of each layer, regardless of the material selected. Accordingly, it would be desirable to develop a microreactor comprising layers that do not require such detailed fabrication.
A patent issued to Bard (U.S. Pat. No. 5,580,523) describes a modular microreactor that includes a series of fluidly connected modules, each module having a particular function (fluid flow handling and control, mixing, chemical processing, chemical separation, etc.). Bard specifically teaches that the plurality of modules are mounted laterally on a support structure, and not stacked, as disclosed by Ashmead. In a preferred embodiment of Bard, silicon wafer technology is again used to etch channels and/or other features into the surface of a silicon wafer. Other disclosed fabrication techniques include injection molding, casting, and micromachining of metals and semiconductor substrates. Again, the processing required to fabricate the individual modules goes beyond merely forming a plurality of openings into each component. Furthermore, the lateral layout of the reactor described by Bard requires a larger footprint than a stacked plate reactor. In Bard""s reactor, the more modules added, the larger the footprint of the entire reactor. In contrast, when additional plates are added to a stacked plate reactor, the footprint of the reactor does not change, which can be a distinct advantage, as in many work environments the area an apparatus occupies on a work bench or floor is more valuable than the vertical height of the apparatus. It would be desirable to provide a reactor design that has a minimal footprint, while still providing the flexibility to add components to customize the reactor for a particular process.
In U.S. Pat. No. 5,961,932 (Ghosh), a reactor is described that is formed from a plurality of ceramic layers, which are fluidly connected, at least one layer including a permeable partition. In particular, Ghosh describes the desirability of sizing fluid channels appropriately to provide for laminar flow and mixing via diffusion, rather than mixing via turbulence. In his preferred embodiment, Ghosh describes that channels, chambers, and passageways are formed in each layer. The particular process Ghosh describes to accomplish this task involves fabricating the layers from xe2x80x9cgreenxe2x80x9d or uncured ceramic, which once shaped as desired, must be sintered. Significantly, the sintering process changes the size of the ceramic layer, so that the sizes of the features formed into the ceramic layer in the initial stages of production are not the sizes of the features in the finished product. It would be desirable to provide a reactor design in which the dimensions of the individual components can be rigidly controlled during fabrication, and not subject to shrinkage, which can negatively effect the dimensions of the finished reactor. This object is particularly important when a reactor design focuses on achieving a laminar flow, because precise dimensional control of fluid pathways in the reactor must be maintained to achieve a consistent laminar flow.
In all of these prior art reactors, relatively complicated manufacturing techniques are required. The manufacture of layers of silicon material requires a large capital investment. Sintering of a ceramic material requires the precise control of the shrinkage process, or individual components of a desired size cannot be achieved. In all cases, the prior art teaches that complicated structures (for example, fluid channels and reaction chambers) must be etched or otherwise fabricated in each layer. Additionally, orifices or passages also need to be formed in each layer, so that fluids can move between adjacent layers of the reactor. Thus, a series of different manufacturing steps typically must be performed for each layer. It would be desirable to provide a reactor design offering the advantages described above, that is relatively simple to manufacture, so as to minimize capital investment in scaling up production from the laboratory to the industrial level. It is therefore an aim of this invention to provide a micro-scale reaction apparatus that can be economically manufactured, can maintain a desired relatively narrow temperature range for a process, has a relatively modest footprint, and can provide efficient diffusion mixing using a precisely controlled laminar flow.
In accord with the present invention, a reactor is defined for reacting one chemical with at least one other chemical, for the purpose of forming a chemical product. The reactor includes a plurality of simple plates, each simple plate having at least one opening formed therein, the simple plates being stacked together to form a plurality of layers and arranges so that at least one opening in each simple plate overlaps at least one other opening in an adjacent simple plate, thereby forming at least one pathway between at least some of the layers.
Preferably, openings within different layers align so as to form at least one inlet port and at least one outlet port, for the receipt and discharge of chemicals, and to form at least one pathway for conveying chemicals to be processed. At least one pathway is formed that is in fluid connection with the inlet and outlet ports, and each simple plate has at least one opening formed in it.
A material from which the simple plates are fabricated is selected for compatibility with the chemical process. In one embodiment, the simple plates are formed from a material selected from the group consisting of crystalline wafers, ceramics, glasses, polymers, composite materials, and metals. Preferably, if formed from a metal, stainless steel is used. The material of the crystalline wafer is selected from the group consisting of silicon and germanium.
It is also preferable that the reactor accommodate a plurality of operations, including temperature control, control of chemical residence time, chemical mixing, and chemical reacting. Temperature control is achieved using a combination of one or more temperature sensors and one or more heat exchangers. Preferably, chemical mixing is carried out by employing pathways sized so that a reactant achieves a stacked laminar flow with respect to at least one other reactant.
In a reactor adapted for processing at least two reactants to form a desired chemical product, an inlet opening for each of the reactants and an outlet opening for the chemical product is provided in at least one of two outer simple plates. An intermediate simple plate is included for mixing the reactants and has at least one opening in fluid communication with each inlet opening and the outlet opening.
Generally, at least one heat transfer fluid inlet port is included in at least one of the outer simple plates, so that at least one heat transfer fluid can be introduced into the chemical reactor. Each heat exchanger is defined by an opening in a different intermediate simple plate. The opening is in fluid communication with the heat transfer fluid inlet and outlet ports and is disposed between adjacent simple plates.
Preferably, each heat exchanger is used to modify the temperature of at least one of the reactants and/or the chemical product. The heat exchangers can be used to modify a temperature of one of two reactants such that they are at different temperatures.
The chemical reactor typically includes a plurality of intermediate simple plates, and the openings in these plates define a first fluid path for a first of the at least two reactants, and a second fluid path for a second of the at least two reactants. Preferably, the plurality of intermediate simple plates define an inter-digital-mixer that separates and aligns the first fluid path and the second fluid path into a plurality of individual fluid paths. The plurality of individual fluid paths are then joined in a laminar flow pathway to provide a stacked laminar flow of the first and second reactants. The stacked laminar flow enables mixing of the reactants to be achieved by diffusion mixing. Preferably, a height of the joined fluid paths is reduced to enhance the diffusion mixing. In at least one embodiment, the height of each individual stacked laminar flow is reduced to less than 50 micrometers.
In one embodiment, a width of the laminar flow pathway is increased, so that a flow rate of a fluid in the pathway remains constant as the height of the pathway is reduced. Preferably, when the inter-digital-mixer separates and aligns the first fluid path and the second fluid path into a plurality of individual fluid paths, a pressure drop for each of the individual fluid paths are substantially equivalent. The inter-digital-mixer also ensures that when the first fluid path and the second fluid path are separated and aligned into a plurality of individual fluid paths, so that each individual fluid path enters the at least one opening in which the individual fluid paths are joined, from the same side.
In one embodiment, the openings in the plurality of intermediate simple plates share common shapes and sizes to the extent possible, to minimize fabrication costs. Preferably, all the simple plates are chamfered at one corner to provide a reference when assembling the simple plates to form the chemical reactor.
Because temperature control of reactants and the resulting product is critical to yield and purity, the chemical reactor preferably includes at least one temperature sensor to monitor a temperature of the product or at least one of the reactants. A temperature sensor is disposed in at least one of the outer simple plates, and another temperature sensor is disposed in at least one of the plurality of intermediate simple plates.
The thickness of the outer simple plates is about 3 millimeters, and that of the plurality of intermediate simple plates is at least about 0.2 millimeters, but not more than about 0.6 millimeters.
In one embodiment, the simple plates are removably held together in the stack by an applied compressive force. In such an embodiment, a housing provides the compressive force, producing a pressure acting on the outer simple plates. The mean surface roughness of the plates should be less than about 1 micrometers, and the simple plates should be substantially free of scratches. The pressure should be greater than or equal to 50 Newtons per square centimeter. In another embodiment, the simple plates are permanently joined. When permanently joined, the mean surface roughness of the plates is preferably less than about 5 micrometers. Permanent joining can be achieved using diffusion welding or vacuum soldering.
Preferably, when the thickness of the intermediate simple plates that are adjacent to a heat exchanger is about 0.3 millimeters. When a series of openings in the simple plates of the chemical reactor defines a fluid path for a heat transfer fluid that flow through more than one heat exchanger, the flow rate and fluid pressure of the heat transfer fluid within each such heat exchanger are substantially.
Another aspect of the present invention is directed to a method for producing stacked plate reactor, which includes steps generally consistent with the apparatus described above.